The invention relates to a mixing device for an exhaust gas recirculation system of an internal combustion engine with an intake air line and an exhaust gas recirculation line, the outlet opening or admission opening of which opens into the intake air line.
A device of the aforementioned type is already known, which provides for centric feeding of the exhaust gas into the charge air line. In this the exhaust gases enter centrically in relation to the intake air flow and in the same direction of flow. At best, however, mixing between exhaust gas flow and intake air flow occurs only in the marginal areas, depending on the relative speed of exhaust gas and intake air. Mixing of the exhaust gases fed in over the short distance between admission point and charge air distributor is therefor very poor, so that the major part of the exhaust gas flow is propagated as far as the last cylinder in the charge air distributor.
German Patent Document DE 43 19 380 C2 discloses an exhaust gas recirculation device for an internal combustion engine with an exhaust turbocharger, with an inlet system, a charge air line, an exhaust system, a return line for an exhaust gas component flow, together with a jet diffuser unit to which charge air is admitted and into which the return line also opens, the jet diffuser unit being arranged directly in the charge air line and the jet diffuser unit, when suitably designed, producing an equilibrium of the pressure differentials between exhaust and inlet system, so that an exhaust gas component flow can be added to the compressed charge air though the return line opening into the jet diffuser unit in the area of a cross-sectional constriction and thereby fed to the inlet system. Optimum mixing of intake air and exhaust gas is not guaranteed, however, because the exhaust gas flows in the marginal area and there is no further additionally generated swirl or turbulence to promote further mixing of the two gas flows.
Accordingly, an object of the invention is to design and arrange the mixing point and/or feed device in such a way that optimum mixing of the exhaust gas with the intake air can be guaranteed.
According to the invention this object is achieved in that a swirl generating element and/or a turbulence generating element is/are provided in the area of the admission opening of the mixing device. As a result the exhaust gas fed to the intake air is optimally mixed in, so that in the downstream mixing zone or mixing line a virtually homogeneous intake air-exhaust gas mixture is produced, in particular because swirling of both gas flows occurs over the entire cross-section of the charge air line.
It is advantageous for this purpose for the swirl generating element and/or the turbulence generating element to be designed as part of a mixing device and as a swirl duct, the swirl duct having internal deflector elements or deflector plates for the exhaust gas in the area of the admission opening and the deflector elements being of helical and/or volute design. The exhaust gas flowing in is set in rotation or is subjected to a swirling movement by the internal deflector plates in the area of the admission opening of the exhaust gas recirculation line, so that optimum mixing of the exhaust gas into the intake air flow is achieved.
According to a development of certain preferred embodiments of the invention an additional possibility is to design the swirl generating element and/or the turbulence generating element of the mixing device as a swirl grille, the swirl grille having deflector elements or deflector plates distributed over the circumference and being arranged in the exhaust gas recirculation line in the area of the admission opening. The deflector plates firstly therefore impart a radial component or a rotational component to the emerging exhaust gas or its direction of flow, so that this superimposition of the two additional flow movements on the existing axial component ensures very efficient mixing of the exhaust gas into the intake air flow.
It is furthermore advantageous according to certain preferred embodiments of the invention for the exhaust gas recirculation line or the admission opening to extend tangentially to the intake air line. Consequently the exhaust gas flow likewise enters the intake air line tangentially. At the admission point this flow movement of the inlet exhaust gas is now superimposed on the intake air flow running essentially axially. As a result this leads to a mixing flow, which has kinetic components both in an axial direction and in a circumferential direction, so that an extremely short mixing distance is achieved.
It is also advantageous according to certain preferred embodiments of the invention for the mixing device to have a baffle element for the exhaust gas in the area of the admission opening, the baffle element being designed as a cone or plate and having deflector elements or deflector plates arranged helically and/or volutely on its surface. The conical baffle element imparts a radial component to the exhaust gas emerging axially from the exhaust gas recirculation line, which radial component, owing to the helical deflector plate, is superimposed on a kinetic component in a circumferential direction. Added to this is a swirling effect on separation of the flow at the end or at the edge of the baffle element. The result is again very efficient mixing of the exhaust gas into the intake air flow.
According to certain preferred embodiments of the solution according to the invention it is further proposed that the exhaust gas recirculation line be of helical, volute, spiral, eccentric and/or concentric design in the area of the admission opening. A rotational impulse or swirl is therefore imparted to the entire exhaust gas flow, optimizing the mixing with the intake air flow.
It is of particular importance according to certain preferred embodiments of the invention that the swirl generating element and/or the turbulence generating element be arranged eccentrically and/or concentrically in the exhaust gas recirculation line and/or in the intake air line in the area of the admission opening. The generation of swirling and/or turbulent motions can be induced in the exhaust gas flow and/or in the intake air flow, since the respective mixing effect is transmitted by the interchange of impulses of the two flows.
In the context of the design and arrangement according to the invention it is advantageous according to certain preferred embodiments of the invention for the admission opening to be designed as a jet or diffuser and arranged coaxially in the intake air line, the ratio of the diameter of the intake air line to that of the exhaust gas recirculation line have a value between three and ten. Mixing can be promoted and the pressure ratio optimized by way of the cross-sectional shape of the admission opening according to the pressure ratios prevailing in the exhaust line and the intake air line.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.